This project aims to examine the trafficking and processing of the amyloid precursor protein (APP) in neurons. APP gives rise the amyloid-p protein (AS),is mutated in a subset of Alzheimer's disease patients, and is the enzymatic substrate of the protease presenilin - the other mutated protein involved in familial Alzheimer's disease. Therefore, elucidating the mechanism by which the processing of APP to A3 is regulated is likely to be crucial to understanding and, subsequently, treating Alzheimer's disease patients. While the trafficking and processing of APP has been thoroughly studied in non-neuronal cells. Remarkably, very basic information is still not known about the specific biochemistry of neuronal APP. This project, therefore, will examine fundamental questions about APP in neurons. The overall hypothesis is that the amyloidogenic processing of APP is regulated by polarized sorting of APP to neuronal processes. Two specific aims will directly test this hypothesis. The first specific aim is to determine if there is a polarized distribution of amyloidogenic APP fragments in neurons. To visualize APP in neurons, APP is fused to a photoconvertible fluorescent protein. Thus, APP containing vesicles will be tracked as they are trafficked through cultured neurons. After characterizing the trafficking patterns of APP vesicle populations, the neurons will be fixed;and these vesicles will be stained for the amyloidogenic APP fragments, which are expected to be distributed in a polarized manner intracellularly. The second specific aim will directly test whether polarized sorting of APP affects APP processing in neurons. For these experiments, APP is fused to targeting motifs that will restrict APP targeting to either the axons or to the dendrites. Metabolic labeling of APP followed by immunoprecipitation will allow the APP fragments to be quantified. Thus, whether Ap is released from axons or dendrites will be determined. This information will help explain AB's effects on synaptic plasticity;and modulating APP trafficking will, perhaps, provide a novel therapeutic target for Alzheimer's disease as modulating. Public Health Relevance: The amyloid precursor protein plays a central role in the development of Alzheimer's disease. Understanding how this protein leads to plaque formation in patients'brains will likely lead to new treatment options. This project will test where the plaque protein is made and released from brain cells